[Wien] ghost bands

[Peter Blaha]

>         I have a supercell(of one K + Ti) self consistent calculation with
> distance of Ti from first K, d(K-Ti)=8.01 au.  In this run, I had set
> d(K-Ti)=5.0 au(no core charge leakage) to begin with (ie RMT=2.5 each)
> and the calculation converged without any ghost bands(u-dot smaller than
> u).I get the expected values.
>
> I wanted to increase the RMT of K and Ti to 4.0 a.u each so that they
> almost touch each other ie d(TM-A1)=8.0 au. I started the calculation all
> over from scratch. This time the calculation is faster than the previous
> run(due to small number of plane waves in the interstitials) but I get the
> QTL-B value very large ie
>
> QTL-B VALUE .EQ.   32.30382   !!!!!!
>
> I understand that such a large value for QTL-B is indeed ghost band
> signature in the scf calculation.

Yes, it really seems to be ghostbands.

Check the case.output2 or *help* files and find out for which atoms and states
the problems occur. I expect it is for K s and/or p.

i) I NEVER used such large spheres so far. In the faq page it is said that
for actinides RMT should be kept smaller than 3.0 bohr. Probably similar
values would apply to your case.

ii) If you really want to use such large spheres you may try to remove
APW+lo for K (keep it only for Ti, put 0 instead of 1 in case.in1) or
reduce RKMAX ?.

iii) Eventually with these large spheres EF is at a "strange" value and
you may have to adjust the energy parameters (because e.g. the semicore and
valence energy parameters are too close for K-p ?)

iv) RMTs are not really "free" parameters, but one must choose them according
to certain rules. Of course large RMTs are always better in terms of speed
and thus should be used if possible, however, when it gets larger than 3 bohr
one must be carefull.

Regards

                                      P.Blaha
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-1-58801-15671             FAX: +43-1-58801-15698
Email: blaha at theochem.tuwien.ac.at    WWW: http://info.tuwien.ac.at/theochem/
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